System for powering a combination of variable burden and fixed burden voltage dependent loads from a high impedance source

ABSTRACT

A regulating function is accomplished to provide a means of powering a combination of fixed burden and variable burden voltage dependent loads from a single high impedance source of power.

United States Patent 11 1 Zulaski 1' Nov. 6, 1973 [54] SYSTEM FORPOWERING A COMBINATION 3,524,124 8/1970 Perkinson 320/39 UX 0 V RIABLBURDEN AND FIXED 3,375,434 3/1968 Shapiro 323/4 92242; 21:22: 5:032:1105%;: i FROM A HIGH IMPEDANCE SOURCE 3,443,191 5/1969 Medlar 320/40 x[75] lnventor: John A. Zulaski, Mount Prospect, Ill.

[73] Assignee: S & C Electric Co., Chicago, Ill. Pri Examiner-J. D.Miller [22] Filed: Dem 20 1971 Assistant ExaminerRobert J. HickeyAttorney-Ronald L. Engel et al. 21 Appl. No.1 209,851

[52] US. Cl. 320/39, 323/4 57 B CT {51] Int. Cl. l-l02p 7/06 Field ofSearch u 320/32, 33, 39, A regulating function is accomplished toprovide a 320/59; 323/DIG- 2, 4, 8; 318/139 means of powering acombination of'fixed burden and variable burden voltage dependent loadsfrom a single References Cited high impedance source of power.

' UNITED STATES PATENTS 3,697,850 10/1972 Heinrich et al. 320/ 59 X 5Claims, 4 Drawing Figures T- '1 C O N 5 TA N T 1 1 BURDEN REGULATOR l f0i I CONSTANT 1 C U RR E NT I I SOURCE J5 l l I FIXED I 1.040 l /9VARIABLE l B U R DE N jj l LO A D H l G H l H U N T l IMPEDANCEREGULATOR I SOU RCE I l I PATENTEDnnv 6191s sun-:1 1 or 2 N B MMD 7 RRA1 Wm I a l I l l l l 1 I I l III 9 1/ m 3 1n n 1 Wm M K w. T ANA TEL $DUTT NRG M wwn um VMRW 3w |||||l|||| l||||ll|| lllll a g 1 mm "M O 0 F L 6HIGH IMPEDANCE SOURCE IMPEDANC HIGH VOLTAGE l SENSING RESISTOR SHUNTVOLTAGE REGULATOR CURRENT ssusme RESISTOR SERIES CURRENT REGULATORTRANSFORMER RECTIFIER FILTER SYSTEM SOURCE POTENTIAL DEVICE PAIENIEDnuv6 I973 SHEET 2 [IF 2 1 SYSTEM FOR POWERING A COMBINATION OF VARIABLEBURDEN AND FIXED BURDEN VOLTAGE DEPENDENT LOADS FROM A HIGH IMPEDANCESOURCE This invention relates, generally, to electrical energy supplysystems and it has particular relation to such systems in which a singlehigh impedance power source energizes a variable voltage dependentburden, such as a chargeable battery and a fixed burden voltagedependent load such as a relay.

A high impedance source of electrical energy inherently has very poorvoltage regulation, i.e., the, output voltage varies greatly for smallchanges in burden. This lack of regulation makes the high impedancesource practically useless as a power source for voltage dependentloads.

Accordingly, among the objects of this invention are: To provide forenergizing a combination of a variable burden and fixed burden voltagedependent load from a single high impedance source of electrical energy;to maintain essentially constant the burden applied to the highimpedance source, independent of the variable load; and to maintainessentially'constant the voltage across the variable burden voltagedependent load.

In the drawings:

FIG. I is a block diagram which illustrates a control system embodyingthis invention.

FIG. 2 illustrates by a block diagram a particular application of thesystem shown in FIG. 1 for use in conjunction with charging a battery.

FIG. 3 shows an example of circuit design details that can be employedfor the system illustrated in FIG. 2.

FIG. 4, sheet 1, illustrates a particular application of the systemshown in FIGS. 2 and 3 for use in connection with a battery that ischarged and is employed for operating a motor mechanism.

Referring now particularly to FIG. I it will be observed that thereference character 10 designates, generally, a high impendance sourcewhich comprises an ideal voltage source 11, i.e., a source having nointernal resistance operating, for example, at 60 Hz through a highresistance resistor 12 to energize conductors l3 and with alternatingvoltage. A fixed load in the form of a resistor 15 is connected betweenthe conductors l3 and 14 as an example of a fixed burden load. Thesystem is arranged to energize a variable burden load 16 through aconstant burden regulator 17.

As pointed out above a high impedance source, such as the source 10,inherently has very poor voltage regulation. In accordance with' thisinvention the constant burden regulator is employed and is illustrated,generally, at 17. It is interposed between the fixed load 15 and thevariable burden 16 and comprises a constant current source 18 and ashunt regulator 19, the latter being connected to theconstant currentsource 18 on the side of the variable burden load 16.

FIG. 2 shows the application of the system illustrated in FIG. 1 forbattery charging purposes. Here the high impedance source 10 has itsoutput applied across fixed burden l5 and to atransformer-rectifier-filter system that is indicated, generally, at 22.The system 22 is arranged to charge a battery 26 which constitutes avariable burden load since it requires a greater charging current at-the.beginning of the charging cycle then is required near the end when thebattery is fully charged. Resistor 26' represents the internalresistance of the battery 26. The battery internal cell voltage isrepresented at 26".

In order to accommodate the variation in charging current for thebattery 26 there is provided a series current regulator that isindicated, generally, at 27. Current flow from it takes place througha-current sensing resistor 28 to the battery 26 and to a shunt regulator29. The voltage drop along the current sensing resistor 28 is applied tothe series current regulator 27 such that the current flow is maintainedessentially constant.

As the internal cell voltage 26" increases on charging, the currentrequirements for the battery 26 decrease and it is necessary to disposeof the excess current available from the series current regulator 27.For this purpose the shunt voltage regulator, indicated generally at 29,is connected across the battery 26 and is under the control of a voltagesensing resistor which also is connected across the battery 26. Therelation between the shunt voltage regulator 29 and the voltage sensingresistor 30 is such that the current flow through the shunt voltageregulator 29 increases as the current demand for charging the battery 26decreases.

It will be understood that various circuit connections can be employedfor the system illustrated in FIG. 2. For example, those illustrated inFIG. 3 can be used.

' Here it will be observed that the transformer-rectifier.-

filter system 22 comprises a transformer, shown generally at 33, havinga primary winding 34 which is connected to a I20VAC l-lz source, forexample, the high impedance source 10 previously referred to. Thetransformer 33 includes a secondary winding 35 which is connected toenergize a full wave bridge rectifier that is indicated at 36. Acapacitor 37 is connected across the rectifier 36 for reducing the A.C.ripple in its output. The rectifier 36 is connected between conductors24 and 25 for charging the battery 26. The current flow to the battery26 is under the control of the series current regulator 27 and the shuntvoltage regulator 29.

For illustrative purposes the series current regulator 27 is comprisedof a series pass transistor 38, driver transistor 41, zener diode 43,field effect transistor 42 and the current sensing resistor 28. Theresistor 28 comprises a series fixed resistor 39 and a variable resistor40, the latter being employed for adjusting the current output of theseries current regulator 27. The series pass transistor 38 is controlledby the driver transistor 41 having associated therewith the field effecttransistor 42 in conjunction with the zener reference diode 43 which isconnected between the variable resistor 40 and the base of the drivertransistor 41.

The shunt voltage regulator 29 is comprised of shunt transistor 46,collector resistor 47, stabilizing resistor 50, zener voltage reference49, comparison transistor 48 and voltage divider 30. The shunttransistor 46 is connected between the conductor 25 and variableresistor 40 through the collector resistor 47 whichlimits the maximumcurrent flow that can be bypassed around the battery 26. The shunttransistor 46 is under the control of the comparison transistor 48 andthe zener voltage reference diode 49 to which the stabilizing resistor50 is connected from conductor 25. A diode 51 is connected between thecollector resistor 47 andthe conductor 25 and across the shunttransistor 46. The shunt voltage regulator 29 is under the control ofthe voltage sensing resistor 30 which includes a variable resistor 52that is connected to the base of the comparison transistor 48 and seriessections 53 and 54. By adjusting the variable resistor 52 the amount ofcurrent flowing through'the shunt voltage regulator 29 and bypassing thebattery 26 can be changed.

The current flow to the battery26 for charging takes place through adiode 55 which prevents reverse current flow and through an ammeter 56which measures the magnitude of the charging current. A diode 57,paralleling the ammeter 56 preserves a continuity of the chargingcircuit should the ammeter 56 become open,

circuited. The positive side of the battery 26 is connected through acapacitor 58 to ground 59. Conductor 25 is connected through a capacitor60 to ground 61.

As pointed out above the series current regulator 27 functions tomaintain a constant current flow through the current sensing resistor 28to the battery 26. The base to emiter voltage of transistors 38 and 41is dependent upon the voltage difference between the zener reference.voltage from the zener diode 43 and the current sensing voltageappearing as the voltage drop across the resistor 28. It will be assumedthat the system is operating and has stabilized, that the battery 26 isdemanding current in excess of that which the series current regulator27 is passing, and that the shunt voltage regulator 29 is not in thecircuit. Should a further increase in current flow to the battery 26 hedemanded there will be a slightly increased voltage drop across thecurrent sensing resistor 28 which tends to turn off the transistors 38and 41. If the current required by the battery 26 decreases, there is acorresponding reduction in the voltage drop across the current sensingresistor 28 and transistors 38 and 41 are driven harder into conduction.It will be seen that the circuit is such that the series currentregulator 27 automatically maintains a fixed voltage drop across thecurrent sensing resistor .28. The main function of field effecttransistor 42 is to provide a constant current source for the zenervoltage reference 43. While a resistor could be employed from collectorto base of transistor 41, preferably the field effecttransistor 42 isemployed since it improves the regulation of the circuit with regard toinput voltage variations.

Since the series current regulator 27 automatically functions tomaintain a fixed current flow to the battery 26 which may require avariable current flow, the shunt voltage regulator 29 is employed tobypass the excess current flow not required by the battery 26.

In describing the functioning of the shunt voltage regulator 29 it willbe assumed that the circuit has stabilized and that the shunt transistor46 is conducting the excess current available from the series currentregulator 2 7 to the return path of conductor 25. As pointed out abovecollector resistor 47 limits the maximum current that can flow throughthe shunt transistor 46. The zener voltage reference diode 49 maintainsa voltage reference for the emitter of comparison transistor 48. Thevoltage sensing resistor 30, which is connected across the battery 26,is employed to sample the voltage appearing across its terminals.Transistor 48 compares the sampled voltage provided at the voltagesensing resistor 52 with the reference voltage provided by zener diode49 and amplfies the difference signal. Resistor 50 stabilizes the zenerdiode 49. If the terminal voltage of the battery 26 should decrease,indicating a need for increase in charging current to the battery 26,then transistor 48 tends to turn off, thereby reducing the base drivefor the shunt transistor 46. This will result in less current beingshunted through the collector resistor 47 and the transistor 46 andallow more current to flow into the battery 26. If the terminal voltageof the battery 26 should increase, indicating a reduction in need forcharging current to it, then transistor 48 is driven harder toconduction, thereby causing transistor 46 to conduct harder. Theresulting increase in current shunted from the series current regulator27 through the transistor 46 and resistor 47 leaves less currentavailable for the battery 26.

The zener reference voltage 49 is selected to have a temperaturecoefficient which, in combination with the temperature coefficients ofthe transistors 46 and 48, compensates for variations in the terminalvoltage of the battery 26 with temperature variations. This avoidsproblems of gassing, water loss and self discharge of the battery 26under high temperature conditions.

FIG. 4 illustrates a commercial application of the system shown in FIG.2 using the circuit connections illustrated in FIG. 3. Here the highimpedance source comprises a resistor Potential Device, that isindicated, generally, at 64. It includes a series transformer, indicatedgenerally at 65, having a primary winding 66 which is connected througha resistor 67 to a high voltage conductor 68. The primary winding 66 isconnected to ground as indicated at 69. The transformer 65 has asecondary winding 70 to which conductors 71 and 72 are connected. Theyare arranged to energize the winding of an undervoltage relay, to bedescribed, and a battery charger that is indicated, generally, at 73.The constant burden battery charger 73 may employ the circuitconnections illustrated in FIG. 3 and described hereinbefore. Thebattery charger 73 is connected to maintain in charged condition abattery 74 which corresponds to the battery 26 in FIGS. 2 and 3 and tothe variable burden load 16 of FIG. 1.

The battery 74 can be employed for various purposes such as foroperating a motor mechanism, indicated generally at 75, that is arrangedto operate a circuit interrupter or circuit breaker between open andclosed positions. The motor mechanism 85 includes a direct current motor76 which is energized when contacts 77 of a motor control 78 are closed.It will be understood that the motor control 78 may be manually operatedor it may be automatically operated by relays. When the contacts 77 areclosed to energize the motor 76, a relatively heavy load or high currentis applied to or drawn from a battery 74. However, the charging currentto the battery 74 is limited by the series current regulator 27 in themanner hereinbefore described while the shunt regulator 29 isessentially open circuited. The system resumes normal operation forcharging the battery 74 on opening of the contacts 77.

For illustrative purposes it is pointed out that the series transformer65 may have a winding ratio of 65 to 1, that the resistor 67 may have avalue of 8.0 Megohms and the conductor 68 may be energized with 60 Hz ata voltage of 40 Kv. The potential device 64 may have an output rating of30 voltamperes at a voltage of 40 Kv. The potential device 64 thenfunctions substantially as a constant current source. In order tomaintain a fixed output voltage, assuming a constant input voltage tothe transformer 65, the burden applied to the secondary winding 70 mustbe constant. In the system shown in FIG. 4 the load comprises the 12volt battery charger 73 and a winding 79 of an under voltage relay thatis arranged to control contacts 80 connected in series with the motorcontrol 78. In the event that the conductor 68 should be deenergizedand, since contacts 80 are then closed, the motor control 78 can beoperated to energize the motor 76. After the motor 76 has performed itsfunction a limit switch 81 is opened to deenergize the motor 76. Underthese circumstances there is no load applied to the battery 74. This isdesirable since the conductor 68 may be deenergizedfor a substantiallength of time. The constant burden battery charger 73 will notdischarge the battery 26 because the diode 55 is blocking.

It will be understood'that the battery charger 73 normally providesproper charging current to maintain the required charge on the battery74 independently of input voltage, temperature and load. The system willbe required to operate under short circuit conditions at infrequentintervals when the motor control 78 is operated to energize the motor76. Thus the voltage across the secondary winding 70 of the seriestransformer 65 is not affected by the load supplied by the battery 74 orthe charge requirements of the battery 74 because of the constantcurrent regulator 27, FIG. 2, included in the battery charger 73.

If the battery 26 is replaced in the field, the battery charger 73 willnot be affected by the open circuit since all of the current'from thecurrent regulator 27 then flows through the shunt regulator 29.

The battery charger 73 employing the circuitry shown in FIG. 3 has thefollowing features:

1. Battery charger input current is not affected by changes in the stateof charge of the battery or load variations, including short circuit andopen circuit.

2. Battery charging rate is automatically controlled by the batteryterminal voltage and state of charge.

3. Fail safe circuitry prevents discharge of the battery in the event ofloss of source voltage or an internal failure of the charger.

4. Charger cannot be damaged by short circuit or open circuit of theoutput terminals.

5. Burden or maximum charge rate adjustment.

6. Regulated output voltage adjustment.

For example, the battery charger 73 can conform to the following:

INPUT SPECIFICATIONS Input Voltage Operating Range 108 VAC-140 VAC Inputfrequency 50-60 Hz 1 Input Current Regulation Effect of Charger Loadinput current will vary less than 1% with charger output load varyingfrom open circuit to short circuit. Effect of Input Voltage inputcurrent varies in direct proportion to input voltage variations. MaximumBurden Adjustment Range 4.0 VA to 17.0 VA Operating Temperature Range 40F to +l60 F OUTPUT SPECIFICATIONS Current Capability 500 ma max. at 13volt D.C. Max. Output Voltage Adjustment 12 VDC to 14 VDC Output VoltageRegulation Line Regulation il% from 108 volt to VAC Load Regulation 11%from 0-130 ma for 8 VA 0-400 ma for 30 VA Temperature coefficient 4mv/CMetering 0-500 ma DC 5% Full Scale Accuracy Terminations 4 pt. terminalblock I claim:

1. In a high voltage alternating current electrical transmission systemhaving a high impedance alternating current source, a fixed burdenvoltage dependent sensing device connected to said alternating currentsource for sensing the voltage of the transmission system by sensing thevoltage supplied by the current source; an electrical energy supplysystem for supplying electrical energy to a variable burden load withoutaffecting the voltage supplied by the alternating current sourcecomprising:

a constant current source means connecting in series circuit relationbetween the alternating current source and the variable burden load forsupplying a constant current to said variable burden; and

a voltage regulator means connected in parallel circuit relationshipwith the variable burden load for shunting the current from saidconstant current source means as said variable burden load varies sothat the voltage supplied by the high impedance source is not affectedby the varations of said variable burden load and so that the sensingdevice can accurately sense the voltage ofv the transmission systemwithout being affected by the variations of the said variable burdenload.

2. An electrical energy supply system as claimed in claim 1 wherein arectifier means is connected across said alternating current source, forrectifying that current supplied by said alternating current source.

3. An electrical energy supply system as claimed in claim 1 wherein saidconstant current source means limits current flow from said alternatingcurrent source when the circuit to said variable burden load is shortcircuited and said voltage regulator means shunts current flow from saidalternating current source when the circuit to said variable burden loadis open.

4. An electrical energy supply system as claimed in claim 1 wherein thevariable burden load comprises a chargeable battery, a motor isenergizable from said battery on closure of normally open contacts, anda motor control energizable from said battery is arranged to close saidnormally open contacts; and the sensing device comprises an undervoltage relay having a winding connected across said alternating currentsource and having normally closed contacts in series with said motorcontrol, said normally closed contacts being held open as long as saidwinding is energized at normal voltage from said alternating currentsource.

5. An electrical energy supply system as claimed in claim 4 wherein saidhigh impedance source is a potential device.

1. In a high voltage alternating current electrical transmission systemhaving a high impedance alternating current source, a fixed burdenvoltage dependent sensing device connected to said alternating currentsource for sensing the voltage of the transmission system by sensing thevoltage supplied by the current source; an electrical energy supplysystem for supplying electrical energy to a variable burden load withoutaffecting the voltage supplied by the alternating current sourcecomprising: a constant current source means connecting in series circuitrelation between the alternating current source and the variable burdenload for supplying a constant current to said variable burden; and avoltage regulator means connected in parallel circuit relationship withthe variable burden load for shunting the current from said constantcurrent source means as said variable burden load varies so that thevoltage supplied by the high impedance source is not affected by thevarations of said variable burden load and so that the sensing devicecan accurately sense the voltage of the transmission system withoutbeing affected by the variations of the said variable burden load.
 2. Anelectrical energy supply system as claimed in claim 1 wherein arectifier means is connected across said alternating current source, forrectifying that current supplied by said alternating current source. 3.An electrical energy supply system as claimed in claim 1 wherein saidconstant current source means limits current flow from said alternatingcurrent source wheN the circuit to said variable burden load is shortcircuited and said voltage regulator means shunts current flow from saidalternating current source when the circuit to said variable burden loadis open.
 4. An electrical energy supply system as claimed in claim 1wherein the variable burden load comprises a chargeable battery, a motoris energizable from said battery on closure of normally open contacts,and a motor control energizable from said battery is arranged to closesaid normally open contacts; and the sensing device comprises an undervoltage relay having a winding connected across said alternating currentsource and having normally closed contacts in series with said motorcontrol, said normally closed contacts being held open as long as saidwinding is energized at normal voltage from said alternating currentsource.
 5. An electrical energy supply system as claimed in claim 4wherein said high impedance source is a potential device.